1. Field of the Invention
The present invention relates to linking gap detecting device and method of an optical recording medium, etc.
2. Description of the Related Background Art
An optical disc such as CD-R, CD-RW, DVD-R, DVD-RW, and DVD-RAM is known at present as a recording medium of an optical type able to write an information signal. Further, an information recording/playing apparatus for recording and playing information data with respect to such an optical disc has been produced as a product.
It is generally possible to examine performance of the optical disc by measuring an error rate in a recording state of the information data. As a result of the measurement, the disc having a high error rate is judged as a bad recording state of the information data.
However, there is a case in which a linking gap is caused in the writable optical disc when new information data are continuously written in a position already written. The linking gap is a gap between a writing portion of the previous information data and a writing portion of the new information data.
In the above error rate measurement, when the linking gap is caused in the optical disc, a PLL circuit for synchronously outputting a read signal is operated and returns the optical disc to a normal play state immediately correspondingly to the next synchronous signal even when no synchronization is taken in this linking gap portion. Thus, the error rate only temporarily becomes worse, but no problem is caused. For example, in the standard of the case of the DVD-RW as an optical disc, it is determined that an LPP (land prepit) exists within the period of the synchronous signal of 14T (T is a unit mark length). The LPP is arranged in advance on a land track to know record timing and an address of the information data when a disc recorder records the information data. When the linking gap is caused, the phase relation of the synchronous signal of 14T and the LPP is shifted, but the PLL circuit is operated so as to recover this phase relation in 14T of the synchronous signal next read. Accordingly, even when the linking gap is caused, it is only a momentary change for the worse in the error rate measurement and this worse is approximately similar to the worse of the error rate caused by dirt and damage. Therefore, it is difficult to specify whether the worse of the error rate is caused by the linking gap.
However, when the amount of the linking gap is large, no standard of the optical disc can be satisfied and no normal play can be performed in an optical disc player which has not any good playing quality. For example, in screen image reproduction, the screen is frozen and a mosaic state is caused. Further, the same portion is repeatedly played in a certain player. Accordingly, it is desired to exactly detect the linking gap portion of the optical disc apart from the error rate measurement.